Opportunistic people hope that their behavior can be concealed; so your kind reminder will leave a shadow in his heart and affect your friendship, even though on the surface he is a little ashamed. Everything remains the same. He is still just a child. It may be his living environment that caused him to behave like this. But when you see his behavior, you want to tell the truth but you are worried that he will hate you. You want to persuade him to go back to the right path but you are worried that it will be in vain. ,Is it right? Since we are good friends, I think you can remind him privately of the seriousness of this behavior and advise him to change as soon as possible. If you think this will hurt him, tell him something about the thief, guide him through the story, and let him understand the seriousness of the situation. I personally think it is better not to tell the teacher. If you know his parents, you can tell his parents and ask them to help you help him get out of the way. As a friend. You should think about him. Think about what would be good to do first. Remind him first. Hope he can correct it. And take the initiative to admit your mistakes. If he doesn't listen. Tell his parents first.